1. Field of the Invention
The subject invention relates to electronic thermostats. More particularly, the subject invention relates to adaptive electronic energy management thermostats having the ability to measure the parameters of a building, its climate control system and its surrounding environment and to optimize the efficiency of energy consumption as a function of these parameters.
2. Description of Related Art
Automated energy management thermostats have progressed in sophistication since their inception. Originally, energy management thermostats merely automated the age-old practice of turning the thermostat down manually when the building was not being used or when the occupants where sleeping, in the case of the residential building.
The automatic, adaptive thermostats progressed in sophistication, as shown by U.S. Pat. No. 4,660,759 to Barnard et al, issued Apr. 28, 1987. This patent discloses a thermostat assembly, which predicts, based on the outside temperature, the inside temperature and the temperature drift rate, which is calculated from measured temperatures from the day before, the time necessary to change the output of the climate control system in order to reach the desired set-point temperature at the desired time. This thermostat assembly recognizes the fact that the conditioned space of an enclosure such as a building will require different amounts of time to achieve the desired set-point temperature at the desired time, and that the varying times are dependant on the surrounding environment. Although this design recognizes the fact that the time required to raise or lower the temperature of a condition space varies as a function of outdoor air temperature, it does not have the capabilities to include other thermal characteristics of the building and the climate control system that have an effect on the time required to reach the desired temperature. Also, inherent in the technique used, is the assumption that the inside air temperature varies linearly with time when the climate control system is on or off. As demonstrated in FIG. 2, the temperature is not linear with time (43),(40).
U.S. Pat. No. 4,897,798 to Cler, issued Jan. 30, 1990 discloses an adaptive thermostat assembly capable of predicting the start up time to activate the climate control system in order to reach the desired setpoint temperature at the desired time. This thermostat assembly recognizes heat transfers are occurring between air inside the building and the outside air, and that thermal energy is stored in the internal walls and contents within the building enclosure. In addition, this thermostat assembly considers the oscillation of temperature during quasi-steady state times, i.e., the times when the thermostat is maintaining a particular set-point temperature, and cycles the climate control system on and off in order to maintain that temperature within a particular range around the set-point temperature. This thermostat assembly does not have the capabilities to include other thermal characteristics of the building and the climate control system that have an effect on the time required to reach the desired temperature because assumptions have been made to simplify the model, the required measurements and the computations.
U.S. Pat. No. 4,432,232 to Brantley et al, issued Feb. 21, 1984 discloses an apparatus and method for measuring the efficiency of a heat pump. The apparatus measures, via temperature sensitive resistance measurements and a wattmeter, the amount of energy input with respect to the amount of energy output in the form of thermal energy. This system is applicable for heat pumps already in operation or it may be incorporated into the design of the heat pump so the apparatus and heat pump may be packaged together as a unit. Although it is of value to know the efficiency of the heat pump, this measurement does not reflect the total efficiency of the climate control system because there are losses in the air distribution system, thus further reducing efficiency.
In summary, none of the prior art discloses an assembly which takes into consideration the thermal parameters which account for the non-linearity of the inside air temperature as a function of time in order to accurately determine the proper start up times to have an enclosure reach a desired set-point temperature at a desired time. Also, none of the prior art discloses an assembly which is capable of predicting, in advance of implementation, the energy consumption of the building's climate control system at the existing outside air temperature, and then optimize the thermostat setback schedule to minimize energy consumption, while satisfying a user-specified occupancy comfort schedule.